The development of the hydrofoil lifting device has the potential to greatly advance the performance of watercraft. Both powered and sail craft may benefit from the application of the hydrofoil device. These performance enhancements have been limited by difficulties associated with the hydrofoil control mechanisms. Previous applications of hydrofoils to sailcraft have also been limited in that the designs were effective only in high wind conditions.
For large powered watercraft, fully electronic control mechanisms have been developed to optimize performance and stability under varying weather and sea conditions. For smaller powered vessels, or for sail boats in particular, the power consumption, weight, and complexity of fully electronic control systems is not as practical. The present invention offers many of the advantages of an electronic control system with a much simpler design, suitable for use even in small power or sailboats.
Previous designs for hydrofoil craft have not fully addressed all the requirements for a control system that accommodates varying weather, sea, and load conditions. One such design (U.S. Pat. No. 6,578,507 to Bergmark) employs hydrofoil devices intended to counteract the heeling force of the wind against the sail. The design does not address altitude stabilization or automatically adjust for changing wind conditions or sail trim (“the wings may be actuated by means of control means that are accessible from the cockpit)”.
In a similar U.S. patent (Baulard-Caugan U.S. Pat. No. 4,385,579) hydrofoil-like devices are linked to the mast to provide some means of compensating for wind variations. This design improves roll stabilization but does not exploit the lifting potential of the hydrofoils to reduce hull drag, nor does it attempt to control the altitude of the craft.
U.S. Pat. No. 3,762,353 (Shutt) is also designed primarily to counteract the heeling force exerted by the sail/mast. The hydrofoil's angle of attacked is controlled by a small float assembly linked to the main hull. This design does not exploit the lifting potential of the hr drofoil, and is also very susceptible to localized variations in wave height that could adversely affect stability.
The catamaran stabilization structure of U.S. Pat. No. 4,561,371 (Kelley et al) employs passive wing structures whose angle of attack is fixed and therefore do not adjust to accommodate changing conditions.
In U.S. Pat. No. 5,168,824 (Ketterman) the hydrofoil control mechanism also makes use of a small “canard” on the water surface near the foil. To reduce susceptibility to localized wave action, a flexible linkage absorbs higher-frequency variations in canard height. The rudder foil does not employ the canard control mechanism, and is therefore less effective in counteracting any pitching motion that may be induced by wind/wave interaction. The canard mechanisms on the lateral foils may also be susceptible to swamping by large waves which could destabilize the craft.
The present invention uses a foil control mechanism which addresses many of the problems of prior designs, while adding additional benefits. Rather than using localized float sensing mechanisms, the new design controls the foils based on the buoyancy along the entire length of two or more hulls. This method minimizes any disturbance from localized wave action and automatically compensates against heeling, pitch, and roll. The buoyancy provided by the hulls combines with the hydrodynamic force from the foils, so that performance is improved even for a sailcraft in low wind conditions.